With the growing popularity of environmental, health-monitoring, and infrastructure applications, wireless sensor networks are being deployed ever-more widely. Low power consumption is, of course, critical to these applications. To conserve energy, one approach is to replace the accurate on-node timer for an always-on wake-up receiver. Such receivers allow the wireless sensor network to operate in a low-power sleep mode. Here, a wireless signal is used to awaken the nodes. At the University of Michigan, Jonathan Brown and David Wentzloff have taken this approach one step further with their clock-harvesting receiver (CRX).
This receiver extracts a 21-Hz clock signal, which is embedded within the GSM standard, for the wake-up of a wireless sensor network. As a result, it does not have to generate that clock within the network. To reduce the energy required for network synchronization, the receiver was designed for heavily duty-cycled operation in a tiered synchronization strategy. It boasts sensitivity of -87 dBm with 57 μs of jitter while consuming just 126 μW power. In sleep mode, the receiver consumes just 81 pW. See “A GSM-Based Clock-Harvesting Receiver with -87 dBm Sensitivity for Sensor Network Wake-Up,” IEEE Journal Of Solid-State Circuits, March 2013, p. 661.